MB39A108 Datasheet, PDF (2/4 Pages) Fujitsu Component Limited. – 5-Channel DC/DC Converter IC with Synchronous Rectification

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MB39A108
s Supports the synchronous rectification method
s Lower starting voltage (CH4 to CH5) : 1.7V
s Power supply voltage range: 2.5V to 11V
s Reference voltage: 2.0Vʶ1ˋ
s Error amplifier threshold voltage:
1.0Vʶ1ˋ (CH1), 1.23Vʶ1ˋ (CH2 to CH5)
s Oscillating frequency range: 200kHz to 2.0MHz
s Standby current: 0ЖA (Typ.)
s Built-in soft-start circuit without load dependency
s Build-in totem-pole type output for MOS FET
s Short-circuit detection from short-circuit input possible
using external signal (-INS terminal)
s Package: TSSOP-38P
Circuit Configuration
Fig.1 shows the block diagram and Fig.2 shows the pin
assignments.
MB39A108 is configured with the following function blocks.
s DC/DC Converter Function
Reference Voltage Generator Block (Ref)
The typical 2.0V reference voltage generated by the generator
circuit is temperature compensated by the voltage supplied
from the power supply terminal and used as the reference
voltage for internal IC circuits. The reference voltage can
supply a load current of up to 1mA to an external device
through the VREF terminal.
Triangular Wave Oscillator Block
The triangular wave oscillator block generates triangular wave
oscillation waveforms from the CT (amplitude 0.4V to 0.9V)
terminal by connecting the condenser for timing and the resistor
at the CT and RT terminals, respectively. The generated
triangular wave is input to the PWM comparator in the IC.
Error Amplifier Block (Error Amp)
The error amplifier detects the DC/DC converter output
voltage and outputs PWM control signals. Stable phase
compensation against the system can be attained by setting up
the optional loop gain through connections of the feedback
resistor and condenser from the output terminal of the error
amplifier to the inverted input terminal.
Possible inrush current at power start-up can be prevented by
connection of a capacitor to the CS terminal of each channel.
By detecting soft-start in the error amplifier, the device
operates soft-start at a fixed timing independent from the
DC/DC converter output load.
PWM Comparator Block (PWM Comp.)
This is a voltage-pulse width modulator that controls the
output duty according to the input/output voltage. The output
transistor stays ON for as long as the error amplifier output
voltage and DTC voltage exceed the triangular wave voltage.
Output Block (Drive)
The output circuit adopts a totem-pole construction and is
Table 1 ON/OFF Setting Conditions for Each Channel
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50 FIND Vol.21 No.3 2003